Frame support for grid



Oct. 19, 1965 MIALE 3,213,313

FRAME SUPPORT FOR GRID Filed 001,. 17, 1961 WITNESSES INVENTOR Goliordo Miole ATTORNEY United States Patent 3,213,313 FRAME SUPPORT FOR GRID Goliardo Miale, Bath, N.Y., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Oct. 17, 1961, Ser. No. 145,548 4 Claims. (CL 313350) This invention relates to electron discharge devices and more particularly to improvements in planar-type electrodes for use in electron discharge devices.

In planar grid electrodes of past design one of the major problems encountered has been that of obtaining a frame structure which is sufficiently rigid to prevent bending or warping when the grid laterals are wound, under tension, onto the frame. Most planar grids, at the present time, are made of a solid strip of metal, usually molybdenum, into which a rectangular hole has been punched. While it has been found that a molybdenum frame of approximately mils thickness is sufiiciently strong to hold the lateral wires in tension without bending, this type of frame has several disadvantages. The most serious disadvantage is that the large area of the frame adds greatly to the interelectrode capacity, particularly the capacity from grid to cathode. To overcome this capacity, some frames have been made in rather complex shapes with a proportionally high manufacturing cost. Even so, these complex shapes often result in a frame which is too weak to properly support the lateral wires in tension.

It is therefore, an object of this invention to provide an improved electron discharge device.

A further object of this invention is to provide an improved electrode structure for use in electron discharge devices.

Another object of this invention is to provide an improved planar-type grid structure for use in electron dis charge devices.

Another object of this invention is to provide an improved planar-type grid structure which when utilized in electron discharge devices permits the reduction of interelectrode capacitance.

A still further object of this invention is to provide a planar-type grid structure which insures a more accurately aligned frame member.

Stated briefly, the present invention provides a rigid frame for planar grid structures by utilizing two substantially parallel, spaced side rods having the grid laterals provided on one side thereof. Cross bars are then positioned near each end of the side rods and are provided with notches at the points at which they are affixed to the side rods. These notches serve the double function of accurately spacing the side rods and also provide for increased contact area of the cross bars with the side rods and hence increase the mechanical strength of the frame.

Further objects and advantages of the invention will become apparent as the following description proceeds and features of novelty which characterize the invention will be pointed out in particularity in the claims annexed to and forming a part of this specification.

For a better understanding of the invention, reference may be had to the accompanying drawing in which:

FIGURE 1 is a sectional view of an electron discharge device employing this invention;

FIG. 2 is a cross sectional view of FIG. 1 taken along the line II--II of FIG. 1; and,

FIG. 3 is an enlarged view in perspective showing a planar-type grid structure as shown in FIGS. 1 and 2 in accordance with this invention.

Referring in detail to FIGS. 1 and 2 there is shown an 3,213,313 Patented Oct. 19, 1965 electron discharge device embodying the present invention in its preferred form. The device or tube shown is a pentode-type vacuum tube and consists of a cathode, a control grid, two beam forming plates, two planar-type screen grids, and anode.

The tube is comprised of an envelope 10 of suitable material such as glass with an electrode assembly indicated generally by the character 12 enclosed therein. The envelope 10 shown is of conventional design and includes a tipped-off exhaust tube 14 on top of the envelope and a button stern header 16 closing off the bottom portion of the envelope. A plurality of metal stems or lead elements 18-22 are sealed through the header 16 and are connected to the elements of the electrode structure 12 within the envelope 10. The lead-in elements (hereinafter referred to as leads) 18-22 not only supply the necessary voltage to the elements of the electrode assembly 12, but also act in conjunction with two spacer elements 24 and 25 to support and space the electrode assembly 12 within the envelope 10.

In the tube illustrated, the electrode assembly 12 includes an electron emissive element or cathode 26 of the indirectly heated type (although it may be of the directly heated type) which is connected by suitable means to a lead similar to leads 18-22 but which has not been shown. A cathode heater 27 is connected by suitable means to a pair of leads 22 (one of which is not shown).

A control grid 28 is positioned around the cathode 26. This control 28 may be of the conventional full wound type and is connected by suitable means to the lead 18. A pair of beam defining plates 30 are positioned around a portion of the control grid 28. These beam deflection plates 30 are substantially U-shaped members made of suitable material, for example nickel plated steel, and serve to restrict the path of the electrons emitted from the cathode 26 to certain areas within the electrode assembly 12. The beam deflection plates 30 are electrically connected together and are connected by suitable means to lead 19.

A pair of screen grids 32, which are electrically connected by the connector 36 and connected to the lead 29, are positioned adjacent the beam deflection plates 30 in such a manner so as to be within the active region of the electron beam as defined by the beam defining plates 30. The screen grids 32 are of the planar frame type, the details of which will be explained more fully with respect to FIG. 3.

An anode 34, of suitable material, for example aluminum clad steel, positioned exterior to and surrounding the aformentioned electrodes, is connected to the lead 21.

For the purpose of spacing the electrode elements of the electrode assembly 12, two spacer elements 24 and 25 are provided. These spacer elements 24 and 25 lie in planes transverse to the plane of the electrode assembly 12 and are usually thin sheets of insulating material such as mica. The spacer elements 24 and 25 are provided with suitable perforations for positioning the elements of the electrode assembly 12 and are positioned within the envelope 10 by means of tabs 38 which abut the internal wall of the envelope 10. The construction and function of the spacer elements 24 and 25 is that which is well known in the art.

With reference now to FIG. 3, there is shown in greater detail an enlarged view of the planar type grid 32 of FIGS. 1 and 2 in accordance with the present invention. This grid 32 comprises two side rods 40 which are held in a spaced relationship by a pair of cross bars 42 located and affixed near the opposite ends of the side rods 40. The rods 40 and bars 42 are made of a suitable material, such as molybdenum and as a typical example have a diameter of approximately 0.030 inch. The cross bars 42 are provided with notches 46 near each end thereof which preferably extend into the cross bars from to A: the diameter of the cross bars 42. The notches 46, which are preferably of arcuate configuration corresponding to the outside surface of the side rods 40, are located at the point of afiixation with the side rods 40 and serve a dual purpose. The first purpose these notches serve is that of accurately locating the spacing between the side rods 40. The second function served by the notches 46 is that of adding mechanical strength to the structure. The side rods 40 and the cross bars 42 are joined together by suitable means, for example by resistance or spot Welding, and it is readily seen that the use of notches provides greater surface areas to be welded together than Would be possible with the contact of two circular members without notches. Additional mechanical strength is gained by the fact that a portion of the cross bars 42 lies in the same plane as that of the side rods. Thus, tensional forces which tend to draw the side rods 40 together are partially counteracted by longitudinal stresses within the cross bars 42 and are not placed upon the weld.

After the side rods 40 and the cross bars 42 have been welded together to form the frame structure, grid laterals 44 are affixed to the opposite side of the side rods 40 from that upon which the cross bars 42 are afiixed. The portion of the structure over which the grid laterals 44 extend is defined as the active area and it is noted that the cross bars 42 are located outside the active area or within the inactive area of the structure. The grid laterals 44 are of suitable material, for example tungsten wire, and would preferably have a diameter of approximately .0004 inch or less. The grid laterals 44 are placed under tensional stress onto the side rods 40 and are affixed thereto by suitable means such as glass frit. It is this tension occasioned by the grid laterals 44, which tends to pull the side rods 40 together.

In the example just given, the frame structure comprising the side rods 40 and the cross bars 42 is of molybdenum and the grid laterals 44 are of tungsten. This selection of materials is advantageous in the operation of the tube in that molybdenum has a greater temperature coefficient of expansion than has tungsten. By virtue of this difference, when the tube is operating and the screen grid is heated, the cross bars 42 will expand to a greater extent than the grid laterals 44 thus increasing the tension and maintaining the spacing of the grid laterals 44.

As the grid laterals are positioned in the tube facing the cathode 26, it is noted that the cross bars 42 are positioned on the opposite side of the support rods 40. This method of positioning the cross bars 42 removes a portion of the frame material away from the cathode 26 and hence will reduce the grid to cathode capacity.

In summary, there has been described a planar-type grid which has, by virtue of the notches in the cross members, a mechanical strength which is superior to those known in the art. The structure thus described is also one which has less grid to cathode capacity by virtue of the fact that a portion of the material of the electrode frame has been removed away from the cathode. These features produce an electrode discharge device which is superior to those generally known in the art.

While there have been shown and described what is at present considered to be the preferred embodiment of the invention, modifications thereto will readily occur to those skilled in the art.

For example, although in the above described embodiment the invention was utilized in a screen grid, it is readily apparent that this invention has equal application in other electrodes such as control or suppressor grids. It is also apparent that a single device may have more than one type electrode embodying the present invention. It is not desired, therefore, that the invention be limited to the specific arrangement shown and describe-d and it is intended to cover in the appended claims all such modifications as fall within the true scope and spirit of the invention.

I claim as my invention:

1. A planar-type electrode comprising side rods, grid laterals provide-d on one side of said side rods, and cross bars affixed to said side rods on the side opposite to said grid laterals, said cross bars having notches on one side thereof at the point of affixation to said side rods to provide for the accurate spacing of the side rods and to provide increased area of contact of said cross bars with said side rods.

2. An electron discharge device comprising, an envelope having an electrode assembly therein, said assembly having at least one planar-type electrode, said planar-type electrode comprising side rods, grid laterals affixed to one side of said side rods, and cross bars transverse and affixed to said side rods to maintain said side rods in a spaced relationship, said cross bars having notches on one side thereof at the point of afiixation with said side rods to accurately position said side rods and to increase the area of contact of said side rods with said cross bars.

3. An electron discharge device comprising an envelope having an electrode assembly therein, said electrode assembly having at least one planar type electrode, said planar type electrode comprising grid laterals provided onto a pair of spaced side rods and fastened to said rods, and cross bars positioned transverse to said side rods and affixed thereto on the opposite side from said grid laterals, said cross bars having notches formed in one side thereof at the point of affixation to said side rods, said notches acting to accurately space said side rods and to increase the contact area of said side rods with said cross bars.

4. An electron discharge device comprising an envelope having an electrode assembly therein, said electrode assembly having at least one planar-type electrode, said planar-type electrode comprising a pair of spaced circular side rods, grid wires provided upon one side of said side rods and affixed thereto to form a series of substantially parallel grid laterals, and a pair of cross bars positioned transverse to said side rods and affixed thereto near each end of said side rods and on the opposite side from said grid laterals, said cross bars being substantially circular in cross section and having notches formed in one side thereof at the point of afiixation with said side rods to accurately space said side rods and increase the area of contact of said cross bars with said side bars, said notches extending into the cross bars between the range of from /3 to /2 the diameter of said cross bars.

References Cited by the Examiner UNITED STATES PATENTS 5/60 Curry et a1. 313350 X 4/62 Kerstetter et a1. 313-350 

1. A PLANAR-TYPE ELECTRODE COMPRISING SIDE RODS, GRID LATERALS PROVIDED ON ONE SIDE OF SAID SIDE RODS, AND CROSS BARS AFFIXED TO SAID SIDE RODS ON THE SIDE OPPOSITE TO SAID GRID LATERALS, SAID CROSS BARS HAVING NOTCHES ON ONE SIDE THEREOF AT THE POINT OF AFFIXATION TO SAID SIDE RODS TO PRO- 